> Re: long discussion about how a neuron works.
This is a good summary.
> Typically this involves travelling down an axon and eventually causing
> other neurotransmitters to be released when the signal arrives.
Yep, my comment was regarding not having nanobots "inside" the
neurons is twofold - (a) I'm not sure how easily they would fit
inside the smallest axon/dendrite bodies without interfering
with normal neuron upstream/downstream transport processes
(there is a lot of traffic in neurons because almost all of
the molecules have to be synthesized in the neuron body and
transported down to the synaptic junctions; and (b) the
power involved in the ion currents in the nerve impluse
may be difficult for a single (or even a group) of nanobots to
suppress.
> The upshot is that it might be possible for a "nanite" (hate that word)
> to sit inside the neuron and release chemicals internally which would
> open the channels and initiate a firing impulse.
It can do the same thing "externally", just pump out a "burst"
of the neurotransmitter into a synaptic cleft.
> More invasively, it might be possible to create artificial channels
> which would reside in the neural membrane and pump ions to stimulate
> or counteract the neural firing.
[Covered in Nanomedicine, section 7.4.5.6 - Outmesssaging to Neurons].
Since the neuron is biased to "fire", triggering it is much easier
than suppressing it. Inject in a few Na+ ions to depolarize the
membrane and it will naturally fire, suppressing a depolarization
once in progress is likely to be difficult.
> I don't have a clear picture of how much room there is
> for all this machinery in the cell or its membrane, though. Maybe it
> would do better to be between the cells if there's more room there.
I think this is going to be true. Robert seems to feel that suppression
of messages such as cyclic AMP production is feasible in normal cells
but he doesn't seem to cover it in neurons. I suspect this is due
to size problems inside neuron appendages and/or heat dissipation problems.
It might be feasible for the nanobots to sit in the cell body and suppress
the incoming ion currents from the dendrites with some really high
capacity pumping.
> As far as VR using this mechanism, you not only have to stimulate the
> sensory neurons (and prevent them from responding to physical stimuli
> that aren't part of the simulation), you also have to inhibit the
> motor neurons, while detecting their firing and feeding that into the
> external-world simulator. So the communication requirements are two-way.
You don't *have* to do this. You could still use the standard joy sticks, pressure suits, etc. to sense the movements of the individual. The sensing & suppression of neuronal output however might make the process more integrated.
> There is also the issue of proprioceptive and vestibular senses, which
> tell you how your body is positioned and oriented. Those too would need
> to be faked with the VR sim.
This is a very good point, and probably points out the distinct advantage
of Nano-VR vs. real-world VR. In the real world, simulating these things
gets expensive (because you have to put the individual in a contraption
that fools these senses). The nanobots can easily give you whatever
sense is required. Pulling 9Gs in a tight turn... no problem.
Robert
Hal